1. Field of the Invention
The present invention relates to integrated circuit packages and packaging methods and, in particular, to packages and packaging methods for light-sensitive integrated circuits.
2. Description of the Related Art
Traditional integrated circuit packages and packaging methods provided for an integrated circuit (also known as a “chip” or “die”) to be connected to an external system and protected from deleterious environmental factors, such as moisture. In order to provide an integrated circuit package of minimum size, it can be desirable to essentially utilize the integrated circuit's semiconductor substrate (e.g., a silicon wafer) as a portion of the package. For example, in “flip chip” packaging processes, bond pads (for the provision of input signals, output signals, supply voltage and ground) on the upper surface of an integrated circuit are directly connected to package bond pads (for example, bond pads on a printed circuit board [PCB]) via solder bumps. During such a flip chip packaging process, an integrated circuit with attached solder bumps is flipped over and aligned with package bond pads. The solder bumps are then subjected to reflow processing in order to attach the bond pads of the integrated circuit to the package bond pads. In this scenario, the semiconductor substrate, on which the integrated circuit was formed, can remain exposed and be used as a portion of a completed integrated circuit package.
FIG. 1 illustrates a portion of a conventional flip chip package 10. Flip chip package 10 includes a printed circuit board 12, an integrated circuit (not shown) formed in and on a semiconductor substrate 14 and solder bumps 16. Solder bumps 16 are attached to bond pads (not shown) on the upper surface 18 of the semiconductor substrate 14. As described above, the solder bumps 16 serve to connect bond pads on the integrated circuit to bond pads (also not shown) on the printed circuit board 12.
A drawback of flip chip packages and packaging processes, and other packages and packaging processes that do not completely enclose the semiconductor substrate and/or integrated circuit with opaque materials, is that the integrated circuit remains exposed to various light sources (e.g., artificial incandescent sources or the sun). For example, an integrated circuit formed in and on a semiconductor substrate may be placed in a non-opaque package to create an esthetically pleasing design for cell phones and other consumer products. These designs, however, expose the integrated circuit to light. For light-sensitive integrated circuits, such exposure can lead to interference with the operation of the light-sensitive integrated circuit, including unwelcome electrical currents/voltages, performance degradation, malfunction or shutdown.
Opaque layers can be applied to the lower surface of a semiconductor substrate after multiple integrated circuits have been formed in and on its upper surface (i.e., when the integrated circuits are in wafer form). However, prior to packaging, integrated circuits in wafer form are diced (for example by being sawn) into individual integrated circuits. The dicing process exposes lateral edges of the semiconductor substrate, through which an integrated circuit can be exposed to light. In addition, the integrated circuit can be exposed to reflected light on its upper surface.
Still needed in the field, therefore, is a package-ready light-sensitive integrated circuit and a process for preparing light-sensitive integrated circuits for packaging that provides for a reduced exposure of the integrated circuit to light. In addition, the process should be simple, inexpensive, and should provide a package-ready light-sensitive integrated circuit of a relatively small size (i.e., a size only marginally greater than the size of a conventional die).